Method and apparatus for bony material removal

ABSTRACT

A method and apparatus is provided for cutting bone. In one embodiment, a femur is resected by means of pattern plates having a cutting path with at least two continuous, non-coplanar guide surfaces. The cutting path has a similar profile to the interior profile of a femoral prosthesis. The cutting path guides a reciprocating, oscillating, or rotating cutting tool along a path for removing material from some or all of the distal femur to accept a distal femoral prosthesis. The cutting tool can be a cylindrical milling bit, and can even have a curvilinear profile to cut bone such that it has a three dimensional profile in cross section. Pattern plates can also be used to cut or remove material from other bones.

RELATED APPLICATIONS

This is a continuation-in-part of application Ser. No. 08/300,379 filedon Sep. 2, 1994 now U.S. Pat. No. 5,574,139.

This application is also a continuation-in-part application of U.S.patent application Ser. No. 08/342,143, filed Nov. 18, 1994 by Haines,et al., now U.S. Pat. No. 5,579,379, which is a continuation-in-partapplication of U.S. patent application Ser. No. 08/300,379, filed Sep.2, 1994, by Goldstein, et al, now U.S. Pat. No. 5,514,139.

This application is also a continuation-in-part application of U.S.patent application Ser. No. 08/479,363, filed Jun. 7, 1995 by Haines, etal., now U.S. Pat. No. 5,643,272, which itself is a continuation-in-partapplication of U.S. patent application Ser. No. 08/300,379, filed Sep.2, 1994 by Goldstein, et al., now U.S. Pat. No. 5,514,139, and which isalso a continuation-in-part application of U.S. patent application Ser.No. 08/342,143, now U.S. Pat. No. 5,597,379, filed Nov. 18, 1994 byHaines, et al., which is a continuation-in-part application of U.S.patent application Ser. No. 08/300,379, filed Sep. 2, 1994, byGoldstein, et al, now U.S. Pat. No. 5,514,139.

BACKGROUND OF THE INVENTION

The entire disclosures of these related applications are expresslyincorporated herein by reference.

1. Field of the Invention

This invention generally relates to a method and apparatus for removingmaterial from bone to create specifically shaped surfaces on or in bone.These surfaces may allow for the interconnection or attachment ofvarious prosthetic devices, allograft or autograft material, or otherobjects either indigenous or foreign to the body.

2. Related Art

Many of the specific applications of the method and apparatus of thepresent invention as described herein apply to Total Knee Replacement, asurgical procedure wherein planar surfaces and/or curvilinear surfacesmust be created in or on bone to allow for proper attachment orimplantation of prosthetic devices. However, it should be noted that itis within the scope of the present invention to apply the methods andapparatus herein described to the removal of any kind of material frombones in any other application where it is necessary, desirable oruseful to remove such material from bones.

Different methods and apparatus have been developed in the past toenable a surgeon to remove bony material to create specifically shapedsurfaces in or on a bone for various reasons including to allow forattachment of various devices or objects to the bone. Keeping in mindthat the ultimate goal of any surgical procedure is to restore the bodyto normal function, it is critical that the quality and orientation ofthe cut, as well as the quality of fixation, and the location andorientation of objects or devices attached to the bone, is sufficient toensure proper healing of the body, as well as appropriate mechanicalfunction of the musculoskeletal structure.

In Total Knee Replacement a series of planar and/or curvilinearsurfaces, or "resections," are created to allow for the attachment ofprosthetic or other devices to the femur, tibia and/or patella. In thecase of the femur, it is common to use the central axis of the femur,the posterior and distal femoral condyles, and/or the anterior distalfemoral cortex as guides to determine the location and orientation ofdistal femoral resections. The location and orientation of theseresections are critical in that they dictate the final location andorientation of the distal femoral implant. It is commonly thought thatthe location and orientation of the distal femoral implant are criticalfactors in the success or failure of the artificial knee joint. Pastefforts have not been successful in consistently and/or properlylocating and orienting distal femoral resections.

Such previous efforts at femoral resections are set forth in thefollowing patents, none of which teach or suggest all of the benefitsand advantages of the present invention. These previous patents include:

Stillwell, U.S. Pat. No. 4,457,307, which discloses a movable saw andsaw carriage which may be mounted to a patient's femur and positioned tocut the femur bone. An elongated rail is secured substantially parallelto the femur. A saw carriage and a carriage housing are attached to therail. The saw has a blade extending substantially parallel to thedirection of linear movement of the saw carriage. The saw carriage isslidably guided along paths substantially parallel to the elongatedrails for making cuts in the femur bone. The saw may be positioned in aplurality of second positions where the saw carriage is slidably guidedin paths substantially perpendicular to the elongated rail for makingtraverse distal femur cuts and for scoring the tibia cortex.Additionally, the saw may be positioned in a plurality of thirdpositions where the saw carriage is slidably guided to form an acuteangle with elongated rail for making anterior and posterior femurchamfer cuts.

Androphy, U.S. Pat. No. 4,487,203, discloses a knee resection systemcomprising a guide member, femur and tibia guide rods, a tibia adaptor,a tibia bar, and a femur bar. After the distal femoral condyles areresected, the guide member is attached to the tibia guide rod extendinginto the tibia. The tibia guide rod has a second guide at a right anglefor receiving the guide member. When properly aligned, the guide memberis fixed to the anterior side of the proximal tibia with pins. The tibiais then resected with an oscillating saw inserted through slots in theguide member.

Rohr, U.S. Pat. No. 4,566,448, discloses a ligament tensor device havinga first member to engage the tibia and a second member to engage theintercondylar notch of a femur and a means for moving the second meanswith respect to the first means for applying a selected tension to theligaments of the joint. Additionally, the invention includes cuttingguide slots for guiding the cutting of the femoral condyles.

Keller, U.S. Pat. No. 4,586,496, discloses a surgical chisel having aflexurally rigid chisel shank and a thin, elongated chisel blade fixedat its front end. A chisel guide is provided having slides fordisplaceably guiding the blade and shank in a longitudinal direction.

Kenna, U.S. Pat. Nos. 4,653,488 and 4,787,383, disclose a tibial cuttingjig for cutting a tibia after the femur has been resected. The tibia isaligned off of the resected femur through longitudinal traction andmanipulation to bring the ankle under the femur to produce a tibialangle of 2.5 degrees resulting in an overall valgus alignment. Thealignment is verified by sight. The knee joint is then immobilized, thetransverse tibial cutting jig is pinned to the tibia, the knee is movedto flexion, and the tibia is cut by resting the saw blade on the topsurface of the cutting jig.

Russell, et al., U.S. Pat. No. 4,722,330, discloses a distal femoralsurface guide for mounting on an intramedullary alignment guide for usein shaping the distal femoral surface. A conventional shaping means suchas an oscillating saw or hand saw is introduced into slots in thesurface guide to resect the femur. The device also includes stabilizingmembers that extend along the sides of the femur to stabilize thedevice.

Fargie, et al., U.S. Pat. No. 4,736,737 discloses a tibial cutting jighaving a base that interconnects with an intramedullary alignment rodinstalled along the axis of the tibia. The base includes outriggerscarrying measurement keys for spacing the base a preselected distanceabove the tibia. A saw guide having slots is attached to the base and ispositioned to allow for the cutting of the tibia, by means of anoscillating saw, at a selected position.

Zarnowski et al., U.S. Pat. No. 4,892,093, discloses a cutting guide fora saw blade for resecting a femur. The device is attached to a femurafter the distal end has been removed and a transverse surface has beenestablished. The cutting guide includes a base member having a planarbase surface. A pair of laterally spaced-apart locating and securingposts are integral with the base member and project in a directionnormal to the base surface to interconnect with the femur. Guide membersin the form of cylindrical bars are positioned within side membersattached to the base. A saw blade may be inserted between the guidesurfaces to properly position the blade to cut the femur.

Vandewalls, U.S. Pat. No. 4,896,633, discloses a drill for drilling ahole into a femur. The device includes a positioning mechanism to firmlyengage the outer peripheral surface of the femoral head and the femoralneck. This immobilizes the drill bushing relative to the femur andorients the axis of the drill with the central axis of the femur.

Whiteside, et al., U.S. Pat. No. 5,002,545, discloses a shaping devicefor shaping the tibial plateau comprising an alignment rod locatedanterior to the anterior cruciate ligament and along the anterior cortexof the intramedullary canal of the tibia. The shaping guide isinterconnected with the rod and is adjustable with respect to the rod tocontrol the amount of resection of the tibial plateau by raising orlowering the cutting guide surfaces. The device includes a pin which isinserted into a hole on the alignment guide for setting rotationalignment by aligning the pin with the intercondylar notch of the femur.

Schmidt, U.S. Pat. No. 5,049,149, discloses a sawing gauge system forintertrochantery accommodation osteotomies for removing a wedge-shapedsection of bone with a predetermined wedge-angle so that an optimalpre-stress load F can act.

Lackey, U.S. Pat. No. 5,053,037, discloses a femoral drill guide withinterchangeable femoral collets, a femoral reamer and a femoralanterior/posterior cutting block with an adoptable anterior femoralledge. A plurality of diagonal slots are provided for making diagonalcuts in the distal end of the femur.

Ferrante et al. U.S. Pat. No. 5,098,436, discloses a modular guide forshaping a femur comprising a first bracket defining a generally U-shapedstructure having an internal surface adapted to be seated on the distalaspect of a resected femur bone and an elongated central openingappointed to expose a selected area of the resected femur, including acurved track for guiding a first shaping tool along a predetermined pathfor controlled shaping of a curved patellar groove and a portion of theselected area exposed through the opening. A second bracket defines alinear slotted bore extending generally parallel to the long axis of thefemur for guiding a second shaping tool to form a relatively deep recessaccommodating an intercondylar-stabilizing housing of a knee implant.

Brown, U.S. Pat. No. 5,234,432, discloses a method of cutting theproximal end of a femur prior to cementing in a prothesis forreconstructive hip surgery.

Poggie, et al., U.S. Pat. No. 5,250,050 discloses an apparatus for usein preparing the bone surfaces for a total knee prothesis, comprisingcutting guides, templates, alignment guides, a distractor and clampinginstruments. The instrument for alignment of the cutting surface forresecting the tibia includes an ankle clamp, an adjustable alignmentrod, and a cutting platform. After the cutting platform is properlyaligned on the tibia, it is pinned thereto and the tibia may be resectedusing an oscillating saw. Also disclosed is a patella resection guidecomprising a scissor-type clamp having distal gripping arms, each ofwhich define a cutting surface, and gripping teeth.

Caspari, et al., U.S. Pat. Nos. 5,263,498, 5,228,459, and 5,304,181disclose a method and apparatus for orthoscopically preparing bonesurfaces for a knee replacement. A tibial jig is attached to the tibiaat just above the ankle at a lower end and to just below the tibialtubercle at an upper end. One portal is formed in the knee for insertionof an orthoscope for viewing the knee, and another portal is formed forintroducing resecting instruments. A cutting platform is aligned andsecured in position and a cutting module is attached. Initially, aplunge cut across the tibial eminence is produced. This procedure isrepeated until the surface of the tibial plateau is covered with trailshaving ridges therebetween. Thereafter, the device is passed back andforth over the tibial plateau to remove the ridges.

Morgan, U.S. Pat. No. 5,269,786, discloses a PCL oriented placementtibial guide method for guiding the tibial tunnel placement both insideand outside the knee in endoscopic ACL reconstruction.

Mikhail, U.S. Pat. No. 5,284,842, discloses a universal patellar clamphaving an articular surface clamping member with a central aperturedefining a centerline axis. An anterior clamping member is positionedalong the centerline axis and is movable with respect to the articularclamping member to effect clamping of the patella for accepting a reamerfor reaming a cavity in the patella of sufficient size to receive apatellar implant.

Johnson et al., U.S. Pat. No. 5,306,276, discloses a tibial resectorguide including a tibial alignment jig having an ankle adjustmentmechanism, a telescoping rod and a tibial resector guide which includesa head having a slot for receiving a bone saw. The head includes angledside walls along the slot which permit the guide to have a narrowanterior aperture, yet allow the saw blade to completely pass throughthe tibia.

Peterson, U.S. Pat. No. 5,342,368, discloses an intramedullary tibialresector guide which is affixed to the tibia by means of anintramedullary rod. An elongated bar extends from the intramedullary rodand carries a sleeve that supports a saw guide having a slot forreceiving an oscillating saw.

Whitlock, et al., U.S. Pat. No. 5,147,365, discloses a patella osteotomyguide comprising a plier-like appliance with curved jaws for grasping apatella. A row of teeth face inwardly from the jaws and a rotatingcalibrated stylus measures the position of the patella with respect toan integral saw capture slot in each of the jaws. The jaws are curvedwith concave inner sides generally corresponding to the shape of apatella. With the guide attached to a patella, a sagittal saw can bepassed through the saw capture slots to cut away a portion of thepatella.

Additionally, Whiteside, U.S. Pat. No. 4,474,177 describes instrumentsfor creating the distal femoral surfaces where a guide is used to indexa flat surface used to guide the distal femoral resection. Kaufman, etal. U.S. Pat. No. 4,721,104 describes a method of preparing theintracondylar area of the distal femur. Jellicoe, U.S. Pat. No.5,047,032 utilizes a side cutting drill to form the distal femoralsurface.

None of these previous efforts, however, disclose all of the benefitsand advantages of the present invention, nor do these previous patentsteach or suggest all the elements of the present invention.

OBJECTS AND SUMMARY OF THE INVENTION

It is a primary object of the present invention to provide a method andapparatus for removing material from bones.

It is another object of the present invention to provide a method andapparatus for properly resecting bone.

It is also an object of this invention to provide a method and apparatusfor properly orienting a resection of a bone.

It is a further object of the present invention to provide a method andapparatus to properly orient the resection apparatus with respect to abone.

It is an additional object of the present invention to provide a methodand apparatus for properly locating a bone resection.

It is a further object of the present invention to provide a method andapparatus to properly locate the resection apparatus with respect to abone.

It is even another object of the resection apparatus of the presentinvention to provide a guide device and method of use thereof forestablishing the location and orientation of the resection apparatuswith respect to a bone.

It is an additional object of the present invention to provide a methodand apparatus for making a curvilinear bone resection.

It is still a further object of the resection apparatus of the presentinvention to lessen the chances of fatty embolisms.

It is even further object of this invention to provide a method andapparatus capable of forming or re-forming some or all of the surfacesor resected surfaces of a bone.

It is another object of the present invention to provide a method andapparatus which is simple in design and precise and accurate inoperation.

It is also an intention of the present invention to provide a method andapparatus for determining the location of the long axis of a bone whilelessening the chances of fatty embolism.

It is also an object of the present invention to provide a method andapparatus to physically remove material from a bone in a pattern.

It is an additional object of the present invention to provide a methodand apparatus to physically remove material from a bone in a patterndictated by a pattern device and/or the geometry of a cutting device.

It is even another object of the resection apparatus of the presentinvention to provide a cylindrical or semi-cylindrical cutting deviceand method of use thereof for removing material from a bone.

It is also an object of the present invention to provide a method andapparatus for easily and accurately resecting a bone.

It is also an object of the present invention to provide a method andapparatus for resecting a bone which minimizes the manual skillnecessary to complete the procedure.

It is even another object of the present invention to provide a methodand apparatus for resecting a bone which is easy to use.

It is still yet another object of the present invention to provide amethod and apparatus for resecting a bone which minimizes the amount ofbone removed.

It is a further object of the present invention to provide a method andapparatus for resecting a bone which allows one to visually inspect thelocation of the cut or cuts prior to making the cut or cuts.

It is yet a further object of the present invention to provide a methodand apparatus for resecting a bone which physically removes materialfrom the bone along a surface dictated by a guide device.

It is still a further object of the present invention to provide amethod and apparatus for resecting a bone which employs a milling bit orform cutter for removing material from the bone.

It is even another object of the present invention to provide a methodand apparatus for removing material from a bone such that both thecutting path and cutting profile are predominantly curvilinear.

These objects and others are met by the method and apparatus for bonymaterial removal of the present invention.

Many of the specific applications of the method and apparatus of thepresent invention described herein apply to Total Knee Replacement, asurgical procedure wherein planar surfaces and/or curvilinear surfacesmust be created in or on bone to allow for proper attachment orimplantation of prosthetic devices. However, it should be noted that itis within the scope of the present invention to apply the methods andapparatus herein described to the removal of any kind of material frombones in any other application where it is necessary, desirable oruseful to remove material from bones.

The apparatus of the present invention comprises a number of componentsincluding a positioning apparatus, a pattern apparatus and a cuttingapparatus.

The pattern apparatus is oriented and located by the use of thepositioning apparatus which references the geometry of a bone to beresected and/or other anatomic landmarks. When used to resect a distalfemur, the positioning apparatus also references the long axis of thefemur. Once the positioning apparatus has been properly located,aligned, and initially fixed in place, the pattern apparatus may beattached thereto, and then adjusted according to the preferences of thesurgeon utilizing the apparatus, and then the pattern apparatus can berigidly fixed to a bone to be resected. This ensures the patternapparatus is properly located and oriented prior to the use of thecutting apparatus to remove material from the bone.

More specifically, when the method and apparatus of the presentinvention are used in connection with resecting a distal femur, thepositioning apparatus is located and aligned utilizing theintramedullary canal of the femur, (thereby approximating the long axisof the femur), the distal surfaces of the femoral condyles, the anteriorsurface of the distal femur, and the posterior surfaces of the femoralcondyles which are referenced to indicate the appropriate location andorientation of the pattern apparatus. Fixation means may be used to fixthe positioning apparatus, as well as the pattern apparatus to thedistal femur. Means may be present in the positioning apparatus and/orpattern device for allowing the following additional adjustments in thelocation and orientation of the pattern device:

1. internal and external rotational adjustment;

2. varus and valgus angular adjustment;

3. anterior and posterior location adjustments;

4. proximal and distal location adjustment; and

5. flexion and extension angular adjustment.

Cannulated screws, fixation nails or other fixation means may then beused to firmly fix the pattern apparatus to the distal femur. Thepositioning apparatus may then be disconnected from the patternapparatus and removed from the distal femur. Thus, the location andorientation of the pattern apparatus is established.

The pattern device possesses slot-like features, or a cutting path,having geometry that matches or relates to the desired geometry of thecut. When used in connection with resecting a knee, the cutting pathresembles the interior profile of the distal femoral prosthesis. Thecutting path, guides the cutting apparatus to precisely and accuratelyremove material from the distal femur. Thus the distal femur is therebyproperly prepared to accept a properly aligned and located distalprosthesis.

In preparing a patella, the pattern device may be an integral part ofthe positioning apparatus which is oriented and located by referencingthe geometry of the patella itself as well as the structures of thepatellofemoral mechanism to determine the location and orientation of apredominantly planar resection. The cutting device may then be employedto perform the resection of the patella by traversing the path dictatedby the pattern device, thus dictating the final location and orientationof the patella prosthesis.

The basic apparatus and method of the present invention is disclosed inthe copending patent applications set forth in the Related Applicationssection of the present application, and the entire disclosures of theserelated applications are expressly incorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

Other important objects and features of the invention will be apparentfrom the following Detailed Description of the Invention taken inconnection with the accompanying drawings in which:

FIG. 1 is a rear perspective view of an embodiment of the patternapparatus of the present invention.

FIG. 2 is a front perspective view of the pattern apparatus shown inFIG. 1.

FIG. 3 is a partially exploded side plan view of the positioningapparatus shown in FIG. 1.

FIG. 4 is an exploded perspective view of the cross bar of the patternapparatus shown in FIG. 1.

FIG. 5 is a partially cut away side plan view of the pattern plate/crossbar attachment linkage for interconnecting the pattern plate to thecross bar as shown in FIG. 1.

FIG. 6 is a perspective view of the positioning apparatus of the presentinvention.

FIG. 7 is a top plan view of the positioning apparatus shown in FIG. 6.

FIG. 8 is an exploded perspective view of the positioning apparatusshown in FIG. 6.

FIG. 9 is an exploded perspective view of the protractor rod guideassembly portion of the positioning apparatus shown in FIG. 6.

FIGS. 10A-10D are plan views of another embodiment of a rod guideassembly for use with the positioning apparatus shown in FIG. 6.

FIG. 11 is a side plan view of an embodiment of the fixation device foraffixing the pattern apparatus shown in FIG. 1 to a bone.

FIG. 12 is a partial side plan view of the pattern apparatus shown inFIG. 1, showing the posterior/anterior referencing guide.

FIG. 13 is a side plan view of another embodiment of the patternapparatus shown in FIG. 1.

FIG. 14 is a side plan view of another embodiment of the positioningapparatus shown in FIG. 6 for use in performing ligament balancing;FIGS. 14A and 14B are cross-sectional views along section A--A in FIG.14.

FIGS. 15A and B are front plan views of an embodiment of the cuttingapparatus of the present invention for cutting a bone a in curvilinearcross-sectional plane.

FIG. 16 is a perspective view of a handle for guiding a milling bitalong a cutting path.

FIG. 17 is a perspective view of another embodiment of the patternapparatus shown in FIG. 1, having a milling bit engaged therewith.

FIG. 18 is a side plan view of the pattern apparatus shown in FIG. 17with the milling bit disengaged from the pattern apparatus.

FIG. 19 is another side plan view of the pattern apparatus shown in FIG.18 showing the milling bit engaged with the pattern apparatus.

FIG. 20 is a perspective view of a femoral implant having a curvedimplant bearing surface.

FIG. 21 is a side plan view of the femoral implant shown in FIG. 20.

FIG. 22 is a side plan view of another embodiment of the patternapparatus and positioning apparatus of the present invention forresecting a patella.

FIG. 23 is a top plan view of the patella resection apparatus shown inFIG. 22.

FIG. 24 is a front plan view of the patella resection apparatus shown inFIG. 22.

FIG. 25 is a perspective view of another embodiment of the patternapparatus of the present invention for cutting a bone.

FIG. 26 is a perspective view of another embodiment of the alignmentapparatus shown in FIG. 6.

FIG. 27 is a partially exploded side plan view of another embodiment ofthe pattern apparatus of the present invention for cutting a bone.

FIG. 28 is a partially exploded perspective view of the interconnectionof a handle with milling bit for use in connection with pattern plateshown in FIG. 27.

FIG. 29 is front plan view of another cutting apparatus for use inconnection with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown generally in FIGS. 1-5, the pattern apparatus of the presentinvention, generally indicated at 30, comprises pattern plates,generally indicated at 32, and cross bar apparatus, generally indicatedat 40.

Pattern Plates

Pattern plates 32 include fixation apertures 34 extending therethroughfor accepting fixation means, as will hereinafter be described, foraffixing the pattern plates 32 to a bone. The pattern plates 32 furtherinclude a cutting path 36 for dictating the path along which a bone isto be cut. As shown in FIGS. 1-5, which are directed to an embodiment ofthe present invention for resecting a distal femur, the cutting path 36in the pattern plates 32 matches the profile of a femoral component of aknee prosthesis for resecting the femur to accept the femoral componentof the prosthesis. Importantly, as will hereinafter be described, thecutting path 36 could be identical in size and shape to an interiorbearing surface of a femoral component of the knee prosthesis, or couldvary in size and shape in accordance with alternative methods andapparatus used to perform the resection. For example, the cutting pathcould be larger than the desired resection, but a larger cutting toolcould be used to arrive at a resection of the desired the desired size.

In the embodiment of the present invention shown in FIG. 3, the cuttingpath 36 includes an anterior end 36A, an anterior cut portion 36B, ananterior chamfer portion 36C, a distal cut portion 36D, a posteriorchamfer portion 36E, a posterior cut portion 36F, and a posterior end36G. Alternatively, the cutting path 36 could of any desired shape inaccordance with the prosthesis systems of the various manufacturers ofsuch prosthesis, the desires of the surgeon utilizing the apparatusand/or the application for which a bone is to be cut.

Although a single pattern plate 32 may be employed in resecting a femuror other bone (and in some cases, i.e. a partial femur resection, it maybe preferable to employ a single pattern plate 32), two pattern plates32 are generally employed to coact with each other to support a cuttingmeans on two sides of a bone to be cut. In the case of resecting afemur, a preferred embodiment of the present invention, as shown inFIGS. 1-3, comprises two pattern plates 32 positioned on opposing sidesof a femur. The pattern plates 32 are interconnected with each other,and maintained in proper alignment with respect to each other by a crossbar apparatus generally indicated at 40, to straddle a bone. The patternplates 32 include cross bar apertures 38 for interconnecting with thecross bar apparatus 40. The pattern plates may also include cross barslots 39 for permitting quick connect/disconnect between the patternplates 32 and the cross bar apparatus 40. Of course, it should be notedthat the pattern plates 32 could interconnect with the cross bar in anyother manner known in the art, or especially with bone cuttingapplications other than resecting the femur, the pattern plates 32 couldbe used without a cross bar.

Cross Bar Apparatus

The cross bar apparatus 40 includes a number of component parts, namely,T-bar 42 having a top 44 and a stem 46 interconnected with and extendingfrom the top 44 in the same plane. The T-bar 42 shown in the Figurescomprises a flat metal member having a uniform rectangular cross-sectionthrough both the top 44 and the stem 46. Three threaded lock apertures48 are formed through the T-bar 42, one at each end of the top 44 and atthe far end of the stem 46. Lock screws 50, having gripable heads 52 andshafts 54 with threaded waists 56, threadably engage the threaded lockapertures 48 in the T-bar 42. The lock screws 50 further include pinholes 58 extending radially through the shafts 54 at the terminal endsthereof for receiving pins 59 for capturing the lock screws 50 on theT-bar 42.

The cross bar apparatus 40 further includes linkages 60 having a firstend for interconnection with the T-bar 42 and a second end forsupporting and engaging pattern plates 32. The first ends of the linkage60 include a lower flat surface 62 for contacting the T-bar 42,overhanging shoulders 64 for contacting the sides of the T-bar 42, andan upper flat surface 66 for contact with the lock screws 50 for lockingthe linkages 60 onto the T-bar 42. As shown in detail in FIG. 5, thesecond ends of the linkage 60 include cylindrical supports 68 forsupporting the pattern plates 32 thereon. The cylindrical supports 68include axial extending apertures 69 for receiving capture pins 70therethrough, the capture pins 70 including flanged ends 72 and threadedends 74. The capture pins 70 serve to capture pattern lock nuts 76 onthe linkages 60, the capture pins 70 extending through the axialapertures 69, the flanged ends 72 retaining the capture pins 70 therein,the threaded ends 74 extending out of the cylindrical supports 69 andinto the threaded interior 77 of the pattern lock nuts 76. Thecylindrical supports 68 receive the cross bar apertures 38 of thepattern plates 32 and the pattern lock nuts 76 are threaded down ontothe capture pins 70 to secure the pattern plates 32 to the cross barapparatus 40. Of course, other embodiments of the cross bar apparatussufficient for supporting the pattern plates of the present inventionare considered within the scope of the present invention.

Positioning Apparatus

As shown in FIGS. 6-10, the positioning apparatus of the presentinvention is generally indicated at 110. The positioning apparatusgenerally comprises positioning body 120 and alignment apparatus 180.The positioning body 120 comprises a frame 122 having sides 124, bottom126 and top 128 arranged to form a frame having a rectangular aperturedefined therewithin. The top 128 further includes a head 130 formedthereon having a linkage aperture 132 extending therethrough at an upperend thereof, and having a lock aperture 134 extending from the upperedge of the head to the linkage aperture 132. A lock screw 136 having athreaded shaft 138 extends into and is threadably engaged with the lockaperture 134 for locking the head 130 to a linkage, namely cross barlinkage 140. Cross bar linkage 140 includes a first end having an upperflat surface 142 for interconnecting with the cross bar in a mannersimilar to the pattern plate linkages for attaching the pattern platesto the cross bar as hereinbefore described. The cross bar linkage 140further includes a shaft 144 which is received by the linkage aperture132 in the head 130 to interconnect the positioning body 120 with thecross bar linkage 140 and hence with the cross bar apparatus 40 and thepattern apparatus 30. The positioning body can then be locked onto thecross bar linkage 140 by means of lock screw 136.

The end of shaft 144 of the cross bar linkage 140 includes projections146 extending axially from the shaft 144. When the shaft 144 ispositioned in the linkage aperture 132, the projections 146 extendbeyond the frame 122 and are received in slots 156 in alignmentindicator 150 for keying the orientation of the alignment indicator 150with the alignment of the cross bar linkage 140, and hence with thealignment of the cross bar apparatus 40 and the pattern apparatus 30.The alignment indicator 150 includes an alignment arrow 152 forindicating alignment on a scale that may be set forth on the positioningbody 120. An indicator pin 158 having a shaft 159 may be employed to pinthe alignment indicator 150 to the cross bar linkage 140.

Attachable to the bottom 126 of the positioning body 120 is skid 160.The skid 160 includes skid apertures 162, one of which may include anaperture flat 164 for insuring proper alignment and positioning of theskid 160 with respect to the positioning body 120. The skid 160 isattached to the bottom 126 of the positioning body 120 by means of skidbolts 166 having threaded shafts 168 which coact with threaded aperturesin the bottom 126 of the positioning body 120. Of course, the skidscould be formed integrally as part of the positioning body.

The sides 124 of the positioning body 120 include slots 170 extending ina facing relationship along the sides 124. The slots extend fromexterior surfaces of the sides to interior surfaces thereof, i.e. to theinterior rectangular aperture formed within the positioning body 120.

Alignment Apparatus

The alignment apparatus 180 interconnects with the positioning body 120by means of alignment guide body 182 which is a U-shaped member havingsides 184 and a bottom 186. The alignment guide body 182 is sized to fitwithin the rectangular aperture formed within the positioning body 120.The alignment guide body 182 is retained within the positioning body bymeans of guide studs 172 that extend through the sides 124 of thepositioning body 120 within the slots 170 and into guide apertures 188at one side of the alignment guide body 182. At the other side of thealignment guide body 182 a lock stud 184 extends through the slot 170 inthe side 124 of the positioning body 120 and into a threaded lockaperture 189 in the alignment guide body 182. The guide studs 172 andthe lock stud 174 coact to maintain the alignment guide body 182 withinthe positioning body 120, and the lock stud 174 can be threaded down tolock the vertical position of the alignment guide body 182 with respectto the positioning body 120.

At upper ends 190 of the sides 184 of the alignment guide body 182 areplate apertures 191. The alignment plate 192 includes bolt apertures 195aligned with the plate apertures 191 of the alignment guide body 182,and plate bolts 194 extend through the bolt apertures 195 in thealignment plate 192 and into the plate apertures 191 to secure thealignment plate 192 to the alignment guide body 182. The alignment plate192 further includes rod guide aperture 197 which receives rod guidebolt 196 therethrough to interconnect the alignment plate 192 with theIM rod guide 210 as will hereinafter be described. Additionally, thealignment plate 192 includes lock slot 206 extending through thealignment plate 192 along an arc for purposes hereinafter described.

The IM rod guide 210 includes IM rod aperture 212 for receiving an IMrod therethrough. The IM rod guide 210 is interconnected at a forwardend with the alignment plate 192 by means of plate attachment aperture214 on the rod guide 210 which receives rod guide bolt 196 therein aftersuch bolt 196 passes through the alignment plate 192 to secure the rodguide 210 in a pivoting relationship with respect the alignment plate192 at forward ends of the rod guide 210 and the alignment plate 192.The IM rod guide 210 is additionally interconnected with the alignmentplate 192 by rod guide lock bolt 200 which includes a threaded shaft 210and pin aperture 202. The rod guide lock bolt 200 extends through theslot 206 in the alignment plate 192 and through threaded lock boltaperture 216 in the rod guide 210 where it is captured by means ofcapture pin 218 extending through the pin aperture 202. The IM rod guidefurther includes rod guide handle 220 which is configured to be easilymanipulated.

The alignment plate 192 further includes a printed angular rotationscale which indicates the degree of angular rotation between the rodguide 220 and the alignment apparatus, and hence the angular rotationbetween the IM rod and the positioning body 120. After such alignment isdetermined, it can be locked into place by tightening down rod guidelock bolt 200. Thereafter, with such angular rotation fixed, the patternapparatus 30 can be positioned with respect to the bone to cut, and thepositioning apparatus 110 can be removed from interconnection with theIM rod and the pattern apparatus 30, the IM rod removed from the bone,and bone cutting can be initiated.

In another embodiment, as shown in FIGS. 10A, 10B, 10C and 10D, IM rodguide block 230 is used instead of the alignment plate 192 and thealignment guide body 182. The IM rod guide block 230 includes a rearsurface 232, a front surface 234, a top surface 236 and sides 238. Thesides 238 include retaining flanges 240 at the rear and front surfacesfor retaining the IM rod guide block 230 within the rectangular apertureformed by the positioning body 120. The IM rod guide block 230 furtherincludes IM rod aperture 242 extending through the block 230 from therear surface 232 to the front surface 234 for accepting the IM rodtherethrough. The rod aperture 242 extends through the guide block 230at an angle A with respect to axis of the guide block for accommodatingthe varus/valgus orientation of the femur. The guide block 230 is partof set of blocks having rod apertures of various angles extendingtherethrough, i.e. 5, 7, 9, 11, 13 degrees, for use femurs havingvarying angles of orientation. The guide block 230 also includes lockaperture 246 for locking the proper vertical position of the guide block230 with respect to the positioning body 220. The guide block 230 mayadditionally include two apertures 244 for accepting an anteriorreferencing arm for use in determining the anterior/posterior size ofthe femur. It should be noted that other alignment means for aligningthe positioning apparatus with respect to a bone to be cut areconsidered within the scope of the present invention.

Fixation Means

Various fixation means, including those known in the art, can be used tofix the pattern plate or plates to the femur or other bone to be cut.FIG. 11 shows a preferred fixation means, generally indicated at 260.The fixation means 260 includes a spike plate 264 carrying on one sidethereof a spike or spikes 262 for contacting, and even extending into,bone 261. At the other side of the spike plate 264 is spike plate socket266 for receiving plate driving ball 268 in a keyed relationshiptherewith. The driving ball 268 is interconnected to an end of drivingsleeve 270 and which has a threaded aperture extending therein from theopposite end thereof.

A driving screw 272 having a threaded shaft 274 coacts with theinternally threaded driving sleeve 270 such that the rotation of thedriving screw 272 either propels or retracts the driving sleeve 270, aswell as the spike or spikes 262, with respect to the driving screw 272.The driving screw 272 further includes a captured head 278 and captureflange 276. The captured head 278 is received within a fixation aperture34 in the pattern plate 32, the capture flange 276 preventing thecaptured head 278 from passing through the fixation aperture 34. Adriving cap 280 is interconnected with the captured head 278 at theoutside of the pattern plate 32. The driving cap 280 includes a shaft282 received by the captured head 278, a flanged head 284 for contactingagainst the outside of the pattern plate 32, and a driver recess 286 ofany desirable configuration for receiving driving means such as a flat,phillips or hex head driving means for driving the driving cap 280 todrive the driving screw 272 to move the spike or spikes 262 towards oraway from a bone.

Importantly, this type of fixation means allows for fixation of thepattern plates 32 to even osteoporotic bones. Additionally, thisfixation means is self adjusting to fit changing contours of bones.Further, because of its relatively low profile, this fixation means doesnot interfere with soft tissue about a bone to be cut. Other types offixation means include cannulated screws, pins, spring loaded screws,captured screws, spiked screws and/or combinations thereof, all of whichare considered within the scope of the present invention and could beused in connection with the present invention.

Anterior/Posterior Referencing

The apparatus of the present invention further includes built-inanterior/posterior referencing means as shown in FIG. 12 for use inconnection with preparation of the distal femur in Total KneeReplacement. As is known in the art, anterior/posterior referencingrefers to proper positioning of the distal femur cuts with respect tothe anterior and/or posterior sides of the femur or other bone to becut.

The anterior/posterior difference between femoral implant sizes may varyby as much as 3 to 5 millimeters between sizes. Of course, many femursare between sizes. Disregarding proper positioning of the cutting guideand the associated femur cuts could lead to flexion contracture (wherethe bone is slightly below size and the implant adds too much materialto posterior side of femur which results in the inability to move theknee into flexion because the extra posterior material contacts thetibial implant components) and/or anterior notching of the femur (wherethe bone is slightly above size and the anterior runout point of theanterior cut is recessed in the anterior side of the bone in a sharpnotch, thus seriously weakening the structural integrity of the distalfemur, especially under cyclic fatigue or impact loading conditions).

Anterior referencing systems have a major advantage over posteriorreferencing systems in that they theoretically never notch the anteriorcortex of the femur. The drawback of anterior referencing is that aslightly larger bone results in collateral ligament laxity in flexionand a slightly smaller bone will result in collateral ligamenttightening in flexion (flexion contracture).

Posterior referencing systems have a major advantage over anteriorreferencing systems in that they theoretically never develop flexioncontracture. The drawback is that a slightly large femur is prone toanterior notching, which can increase the likelihood of distal femoralfractures under either impact loading or cyclic fatigue loading.

Another approach to anterior/posterior referencing is a hybrid designthat allows for both anterior and posterior referencing The positioningapparatus 110 references the posterior femoral condyles (posteriorreferencing), while the pattern plates 32 allow for precise referencingof the anterior femoral cortex. The anterior referencing device can beas simple as that shown in FIG. 12 wherein a referencing pin 294 isplaced through the anterior-most cutting paths 36 of the pattern plates32 to contact the anterior femoral cortex 261. The pattern plates 32include markings S (smaller size) and L (larger size). When the pin 294falls between the S and L marks, the pattern plates 32 are the propersize and are properly positioned for that femur. If the pin 294 fallsoutside the range marked by S and L towards the S side, a smaller sizepattern plate should be used, and conversely, if the pin 294 fallsoutside the range on the L side, a larger size pattern plate should beused. Alternatively, the pattern plate 32 could be adjusted verticallyvia means not shown to compensate for between size bones.

In another embodiment, the pattern plate could include a plungerassembly at the anterior end of the cutting path. The plunger could bemovable vertically to contact the femur and indicate size of the femurwith respect to the pattern plate in use. As such, the plunger could beincrementally marked from +4 to -4 millimeters with 0 being the propersize for the pattern plates in use. Again, the pattern plates could besized up or down if the femur is off of the scale, or the pattern platescould be moved up or down to compensate for between size bones dependingupon surgeon preference. If, for example, a bone registers a +2,anterior notching of the femur would occur. To avoid this, the patternplates could be moved anteriorly 1 millimeter to +1. In this manner,anterior notching would be minimized and the posterior femoral condyleswould only lack 1 millimeter of material, which should not bedetrimental because some ligamentous laxity in flexion is acceptablebecause the collateral ligaments are normally slightly looser in flexionthan they are in extension. It should be noted that the radii or curvein the anterior-most area of the cutting path will assure that anteriornotching is easily avoidable.

Pattern Plate with Tracking Means

Another embodiment of the pattern plates of the present invention isshown in FIG. 13. In this embodiment, the pattern plates, generallyindicated at 310, basically comprise only the lower edge, or bearingsurface 316 of the cutting path 36 of pattern plates 32 shown in FIGS.1-3. Accordingly, the pattern plate 310 includes fixation apertures 312and cross bar aperture 314. The milling apparatus bears against thebearing surface and follows the same therealong to resect the bone inaccordance with the shape of the bearing surface 316. Of course, thebearing surface could be smaller or larger than the desired cut locationdepending on the size of the milling apparatus. The pattern plate 310could further include a groove or guide means 318 extending in thepattern plate alongside the bearing surface and the milling apparatuscould include an arm or other retaining linkage 317 extending from thehandle or bushing of the milling apparatus and into the groove 318 forengagement with the groove 318 for guiding or retaining the millingapparatus along the bearing surface 316 of the pattern plate 310.Alternatively, it should be noted that the bearing surface could alsocomprise just the upper surface of the cutting path 36 of the patternplates 32 shown in FIGS. 1-3.

Ligament Balancing

As shown in FIG. 14, an alternative embodiment of the alignment guidebody 330 can be used for performing ligament balancing. The alignmentguide body 330 of this embodiment can include a skid 332 formed as apart of the guide body 330, or attachable thereto. The skid 332 is of arelatively thick cross section, approaching or equal to the crosssection of the guide body 330. The guide body 330 is attached to thefemur 261 and the femur may be moved from extension to flexion and back,while the ligament tension of the collateral ligaments is reviewed.Ligamentous release can be performed to balance the ligaments. Further,shims 336, in either a rectangular cross section (FIG. 14A) or an angledcross section (FIG. 14B), can be used in connection with the alignmentguide body 330 and skid 332. These shims could be positioned between theunderside of the skid 332 and the resected tibia.

Milling Means

In a preferred embodiment of the invention, a cylindrical milling bit isused for following the cutting path described in the pattern plates forresecting a bone. Importantly, it is within the scope of the presentinvention to use a flat reciprocating bit, much like a hack saw, forfollowing the cutting paths described in the pattern plates forresecting a bone.

Further, it may desirable to make all or some of the cuts using acylindrical milling bit or a flat reciprocating bit having a smoothcenter section without cutting means. An advantage of a cutting toolwithout cutting means along a center portion thereof is the protectionof posterior cruciate ligament during resection of the femur.Accordingly, one cutting tool could be used to make the anterior cut,the anterior chamfer, the distal cut and the posterior chamfer, whileanother cutting tool, with a smooth center portion, could be used tomake the posterior cut to avoid any chance of jeopardizing the posteriorcruciate ligament.

Additionally, the milling bits herein described can be used with orwithout a guide handle as will hereinafter be described. Further, itshould be pointed out that is within the scope of the present inventionto fabricate the milling bit or other cutting tool from metal asheretofore known, or to alternatively fabricate the milling bit or othercutting tool from a ceramic material. An advantage of a ceramic millingbit or cutting tool is that such resists wear and accordingly would be anon-disposable component of the present invention which would help toreduce the cost of the system of the present invention.

Three Dimensional Shaping

Initially, it should be noted that the term cutting profile the profilegeometry of a mediolateral section taken normal to the cutting paththrough the bony surfaces created by cutting the bone. As shown in FIG.15, in an alternate embodiment of the present invention, a millingapparatus having a three dimensional profile, or a form cutter, can beused to shape a bone in three dimensions. The curved profile milling bit350, like the milling bits used in the previous embodiments of thepresent invention, includes cutting teeth 352 along the length thereofand spindles 354 at the ends thereof. This milling bit 330 can follow apattern described by pattern plates and can be guided with a handle aswill be hereinafter described.

Importantly, by using a milling bit having a curved profile, one can cuta femur to resemble the natural shape of the femur, i.e. the resectedfemur would include condylar bulges and a central notch. This wouldreduce the amount of bony material that must be removed from the femurwhile maintaining the structural integrity of the femur. Of course, anyprosthetic implant used for attachment to a femur resected by the curvedprofile milling bit would necessarily have an appropriately contouredinner fixation surface for mating with contoured surface of the femur.Additionally, it should be noted that the curved profile milling bitcould have one or more curvilinear bulges along the length thereof asshown in FIG. 15, or alternatively, could have one or more bulgesdiscretely formed along the length thereof as shown in FIG. 17.

Guide Handle

As shown in FIG. 16, a guide handle, generally indicated at 298 may beused to guide the milling bit along the cutting path of the patternplate. The guide handle 298 comprises a grip portion 300 which isgrasped by the user for manipulating the guide handle 298 andaccordingly, the milling bit. The grip portion 300 is interconnectedwith a crossbar member 302 which includes a extension member 303telescopically interconnected therewith. The crossbar member 302 and theextension member 303 may be positioned perpendicular with respect togrip portion. The extension member 303 is telescopically movable in andout of crossbar member 302. Means may be provided for locking therelative position of the extension with respect to the crossbar. Also,it should be noted that the grip portion may rigidly or pivotallyinterconnected with the crossbar as desired.

Extending from outer ends of the crossbar 302 and the extension member303 are sidebars 304 in facing and parallel relationship. The sidebars304 have two ends, the first of which are interconnected with thecrossbar and the extension member, and the second of which areconfigured to receive and capture spindles or bushings of a milling bitin spindle bushings 306. The spindle bushings are positioned in facingrelation and could include captured bushings. The captured bushingsreceive the spindles of a milling bit. The captured bushings are sizedbe received by the cutting path in the pattern plates and coacttherewith to guide a milling bit therealong. Accordingly, after thepattern plate or plates are attached to a bone, the milling bit placedinto the cutting path. Next a milling handle 298 is positioned such thespindle bushings are aligned with the spindles of the milling bit. Next,the extension is actuated to retract into the crossbar to move thespindle bushings onto the spindles of the milling bit where they arecaptured. Next, the spindle bushings are positioned within the cuttingpath of a pattern plate or plates. If necessary, the extension and crossbar can be locked down to lock the entire apparatus. Next, the millingbit is actuated and the grip portion of the handle is grasped andmanipulated to move the milling bit along the cutting path to cut abone.

Distally Positioned Pattern Plate

As shown in FIGS. 17-19, in an alternate embodiment of the presentinvention for resecting a femur, the plate plates could take the form arail assembly, generally indicated at 400, positioned distally of thedistal femur 261. The plates could be affixed to the femur by fixationarms 402, attached at one or more points to the rail assembly 400, andincluding fixation apertures 404 for receiving fixation screws or otherfixation means for attaching the fixation arms 402, and hence the railassembly 400, to a distal femur 261. The rail assembly 400 includes oneor more guide rails 406 which match the shape of the desired resection,though the rails may be larger or smaller depending on the dimensions ofthe milling apparatus used and the positioning of the assembly 400 withrespect to the femur. In the case that the assembly 400 includes twoguide rails 406, as shown, an end rail 408 may be used to interconnectsuch guide rails 406. The end rail 408 could be replaced by a connectionmeans similar to the cross-bar apparatus 40 hereinbefore described. Therail assembly may be positioned on the distal femur in accordance withthe teachings contained herein or in any other manner known in the art.After alignment according to any means disclosed herein or known ordeveloped, and after fixation of the assembly to a femur, a milling bit420 may be used to follow the guide rails 406 to resect the femur 261,the guide spindles 422, or bushings (not shown), of the milling bit 420,contacting and riding the guide rails 406. Importantly, the railassembly 400 is attached to a femur and used in much the same way as thepattern plates previously described with the exception that railassembly can be positioned substantially distal of the femur, therebypotentially requiring less exposure and possibly resulting in lessinterference for placement thereof. The rail assembly 400 could furtherinclude an upper retaining rail for forming a slot or cutting path forcapturing the milling bit therein. Additionally, it should be noted thatany milling bit described herein could be used with rail assembly 400including a curved profile milling bit.

Curvilinear Implants

As shown in FIGS. 20 and 21, an implant 440 may have curvilinearinterior surfaces 442 as well as a more conventional curvilinearexterior surface. The particular example cited herein is a femoralimplant used in total knee arthroplasty but the principles describedherein may be applied to any application where foreign or indigenousmaterial is affixed to an anatomic feature. The curvilinear bonesurfaces necessary for proper fixation of such an implant may begenerated through the use of the curvilinear milling or form cutter andthe curvilinear cutting path means discussed herein. While it ispossible to use multiple form cutters with differing geometries andtherefore an implant with an internal geometry that varies along thecutting path from the anterior to the posterior of a femur, for the sakeof intraoperative time savings a single form cutter is preferable.

The mediolateral cross-sectional internal geometry of such an implant,and therefore the necessary resected bony surfaces of the femur, areconsistent about the cutting path in a single form cutter system. Itshould be noted that the implant may possess a notch between members 444(posterior femoral implant condyles) in the areas approximately inbetween the distal and posterior femoral condylar areas to accommodatethe posterior cruciate ligament and other factors. Because of the notchbetween the posterior femoral condyles it may not be necessary for theform cutter to cut any material in the notch. It may be desirable toprovide outer flat surfaces 445 with an adjoining curvilinear surface442 positioned therebetween. Other combinations of flat or curvilinearsurfaces are also within the scope of the present invention.

Additionally, it may be advantageous to utilize a secondary form cutteras shown in FIG. 29 for use in creating a slot or slots in or near thedistal area of the femur after it has been resected. Such a secondarycutter 450 would include engagement means 452 for engagement withdriving means, and a shaft 454 carrying cutters 456 for cutting slotsinto the femur through one or more of the resected surfaces thereof.Through the inclusion of an additional or adjunct cutting path in thepattern means, it would be advantageous to utilize the form cutter tocreate the aforementioned slots to accommodate the fixation fins whichmay be molded as an integral part of the interior surface of theimplant. These fins would provide mediolateral fixation stability inaddition to that provided by the trochlear groove geometry of theimplant. Further, the fins also provide for additional surface area forbony contact and ingrowth to increase implant fixation both in cementedand cementless total knee arthroplasty.

There are numerous advantages to the femoral component herein described.Foremost, it will allow for the thinnest implant cross-section possible(perhaps 3 mm to 6 mm in thickness) and therefore necessitate theremoval of the least amount of viable osseous tissue. This is especiallycritical in situations where the probability of revision surgery is highand the amount of viable bone available for revision implant fixationand apposition is a significant factor in the viability of the revisionprocedure. Since the form cutter configuration allows for similaramounts of tissue to be removed from the trochlear groove, the bonyprominences surrounding the trochlear groove, the femoral condyles, andthe other articular surfaces of the femur, the external geometry of thefemoral implant can be optimized for patellofemoral articulation as wellas tibiofemoral articulation. In essence, the kinematics of theartificial joint could be made to be as close as possible to that of ahealthy, natural knee joint. In addition, the curvilinear geometry ofthe implant dramatically decreases the stress risers inherent inconventional rectilinear femoral implants and allows for a thinnercross-sectional geometry while potentially increasing the resistance ofthe implant to mechanical failure under fatigue or impact loading.Conversely, the curvilinear geometry of the implant may also allow foran advantageous reduction in the flexural rigidity of the implant whichmay result in avoidance of the "stress-shielding" inherent in rigidimplant designs. Stress shielding being a phenomenon that may occur whenliving bony tissue is prevented from experiencing the stresses necessaryto stimulate its growth by the presence of a stiff implant. Thisphenomenon is analogous to the atrophy of muscle tissue when the muscleis not used, i.e. when a cast is placed on a person's arm the muscles inthat arm gradually weaken for lack of use.

Additionally, the curvilinear implant design may allow for the use of aceramic material in its construction. Since ceramics are generallyrelatively weak in tension, existing ceramic implant designs containvery thick cross-sections which require a great deal of bony materialremoval to allow for proper implantation. Utilization of ceramics in thecurvilinear implant will not only allow for the superior surfaceproperties of ceramic, but also avoid the excessively thickcross-sections currently required for the use of the material.

This could result in a less expensive femoral implant because of thereduced amount of material needed for the implant, as well as animproved, more natural, and even stronger knee replacement. It maydesirable to vary the cross-section of the implant 440 to assist inseating the implant and to increase the strength and fit of the implant.The implants of the present invention having curvilinear implantsurfaces could be fabricated of metal, plastic, or ceramic or any othermaterial. Further, the thickness of the implants and the materialrequired to fabricate the implant could be reduced as the implants areadapted to increasingly curvilinear surfaces. Also, it should be pointedout the such implants with curvilinear implant surfaces require lessbone to be removed to obtain a fit between the implant and the bone.Finally, it should be noted that curvilinear milling bits hereinbeforedescribed would work well for preparing a bone to receive an implantwith curvilinear interior implant surface.

Patella Shaping

The apparatus for preparing a patella, as shown in FIGS. 22-24,comprises a plier-like patella resection apparatus generally indicatedat 500. The patella resection apparatus 500 includes grip handles 502for manipulating the apparatus, cross-over members 504 pivotallyinterconnected with each other by pin 506, and patella clamp members 508extending from the cross-over members in parallel and facing relation.The patella clamp members 508 have beveled edges 510 for contacting andsupporting a patella along the outer edges thereof. Guide memberstructures 512 are mounted on each of the patella clamp members 508 toform a retainer for a cutting means to follow a cutting path defined bythe upper surface of the clamp members. Bushings 514 are captured inwithin the retainer and the cutting path for receiving a cutting means516 and guiding the cutting means 516 along the cutting path.

In preparing the patella, the pattern device may be an integral part ofthe positioning apparatus which is oriented and located by referencingthe geometry of the patella itself as well as the structures of thepatellofemoral mechanism to determine the location and orientation of apredominantly planar resection. The cutting device may then be employedto perform the resection of the patella by traversing the path dictatedby the pattern device, thus dictating the final location and orientationof the patella prosthesis.

Bone Substitution and Shaping

Referring now to FIG. 25, another embodiment of the pattern apparatus ofthe present invention for cutting bone is shown. This embodiment of theinvention includes pattern plates 532 having cutting paths 536 describedtherein. The pattern plates 532 may be positioned on a bone 528 having atumor or other pathology 529 associated therewith. The pattern plates532 may be interconnected by cross bars 538 with opposing pattern plates(not shown) positioned on the opposite side of the bone 528. Further,each set of pattern plates 532 could be interconnected by means ofpositioning rod 539 extending between the cross bars 538 to maintain therelative location and orientation between the sets of pattern plates532. The pattern plates can be positioned along the bone in accordancewith what is known in the art, disclosed herein or hereafter developed.After the pattern plates are properly positioned, they can be affixed tothe bone 528 with fixation means extending through fixation apertures534. After the pattern plates are properly located and affixed to thebone, cutting can commence by traversing a cutting means along thecutting paths 536 of the pattern plates 532. By this step, the tumor orother pathology 529 can be cut from the bone 528 and a bone graft orother surgical procedure can be implemented to repair and/or replace thebone that has been cut. The benefits of cutting a bone with the patternplates of the present invention include providing smooth and even cutsto the bone to facilitate fixation of bone grafts or other means forrepairing and/or replacing bone. Further, the same pattern plates can beused to cut another identical sized and shaped bone for grafting to thefirst bone to replace the cut away bone.

Alternate Positioning and Alignment Guide

An alternate positioning and alignment guide is generally indicated at620 in FIG. 26. The positioning body 620 comprises a cross bar linkage640 and an alignment indicator 650 at an upper end thereof forinterconnecting with a cross bar to align pattern plates interconnectedwith such cross bar. The positioning body 620 also includes an alignmentblock 680 for interconnecting with an intramedullary rod in much thesame manner as the IM rod guide block shown in FIG. 10. The alignmentblock 680 is vertically movable along the positioning body 620 and canbe locked into a desired position by means of lock screw 700 which bearsagainst a flange 684 of the alignment block 680. The positioning body620 further includes skids 660 for contacting the posterior surface ofthe distal femoral condyles for referencing same.

Unicondylar and/or single pattern plate support

As shown in FIGS. 27 and 28, one pattern plate of the present inventioncan be used by itself to guide a cutting means along a cutting path tocut a bone. Such an application is particularly useful for unicondylarresecting of a femur. Use of a single pattern plate 732 is facilitatedby bushing 760 having an outer flange 762 with a bearing surface 764 andan internal bore 766 sized to receive a spindle 754 of a cutting tooltherein. The bushing 760 is sized to fit into the cutting path 736 ofthe pattern plate 732, the bearing surface 764 of the flange 762contacting the side of the pattern plate 732. Washer 770 includes acentral bore 772 sized to received the far end of the bushing 760extending past the pattern plate 732, the washer bearing against theside of the pattern plate 732 opposite the side that the bearing surface764 of the flange 762 of the bushing 760 bears against. Thus the washerand the bushing coact to form a stable link with a pattern plate. Asshown in FIG. 28, this link can be fortified by means of bearing arms780 interconnected with the bushing and the washer, or formed integrallyas part thereof, which by pressure means are forced together to retainthe bushing within the cutting path of the pattern plate. After thebushing is captured within the cutting path, the spindle of the cuttingmeans can be inserted through the bushing and interconnected with means756 for driving the cutting means. Alternatively, it should be pointedout that when using a single pattern plate to cut a bone, it may bedesirable to support the cutting means at the pattern plate and also atthe other end thereof. One could effect such desired support at theother end of the cutting means by a brace or other linkageinterconnecting the other end of the cutting means with a secondarysupport or anchor means positioned on the opposite side of the bone orat another location.

Revisions

Conventional revisions require removal of the old implant and thereferencing of uncertain landmarks. Revisions by means of the presentinvention allow for reference of the implant while it is still on thebone. One can obtain varus/valgus referencing, distal resection depth,posterior resection depth and rotational alignment by referencing thegeometry of the implant with the alignment guide. An extramedullaryalignment rod can be used to facilitate flexion/extension alignment. Thefixation screws can then be advanced to touch the bone and mark theirlocation by passing standard drill bits or pins through the cannulationsin the fixation screws and into the bone. Then, the pattern and guidedevice are removed, the old implant removed, and the pattern devicerepositioned by means of the marked location of the fixation screws andthen fixed into place. Accordingly, the cuts for the new implant, andthus the new implant itself, are located and orientated based off of theold implant. This results in increased precision and awareness of thefinal implant location and orientation as well as potentialintraoperative time savings.

Modifications of the foregoing may be made without departing from thespirit and scope of the invention. What is desired to be protected byLetters Patents is set forth in the appended claims.

What is claimed is:
 1. An apparatus for cutting a bonecomprising:pattern means including a planar contact face, the patternmeans positionable alongside a surface of a bone to be cut; cutting pathmeans described in the pattern means, the cutting path means comprisingat least two continuous guide surfaces for making non-coplanar surfacesin bone; and cutting means coacting with the cutting path means thecutting means retained by the cutting path means and maintained in aposition normal to the planar contact face of the pattern means whilecutting said non-coplanar surfaces in said bone.
 2. The apparatus ofclaim 1 wherein the cutting means traverses the cutting path means. 3.The apparatus of claim 1 wherein the cutting means is continuously movedalong the cutting path means.
 4. The apparatus of claim 1 wherein thecutting path means comprises more than two continuous, non-coplanarguide surfaces.
 5. The apparatus of claim 1 wherein the cutting meanscomprises a form cutter having a geometry radially concentric about itslongitudinal axis.
 6. The apparatus of claim 1 wherein the pattern meanscomprises opposing pattern plates positionable along sides of a bone. 7.The apparatus of claim 1 wherein the pattern means is positionable alonga side of a femur at a distal end thereof for preparing a femur foraccepting a knee prosthesis.
 8. The apparatus of claim 7 furthercomprising positioning means for positioning the pattern means withrespect to a bone.
 9. The apparatus of claim 8 wherein the pattern meanscomprises opposing pattern plates positionable along sides of a bone.10. The apparatus of claim 9 wherein the pattern plates are positionableto straddle a bone.
 11. A method for cutting a bone comprising the stepsof:positioning pattern means alongside a surface of a bone to be cut,the pattern means including a planar contact face, the pattern meansincluding a cutting path having at least two continuous guide surfacesfor making non-coplanar surfaces in bone; affixing the pattern means toa bone; interconnecting a cutting means with the pattern means;retaining the cutting means normal to the planar contact face of thepattern means; and traversing the cutting means along the cutting pathof the pattern means and maintaining the cutting means normal to theplanar contact face of the pattern means to cut non-coplanar surfaces ina bone.
 12. The method of claim 11 further comprising the step ofmanipulating the cutting means to continuously traverse to the cuttingpath.
 13. The method of claim 11 wherein the pattern means comprisespattern plates and the step of affixing the pattern means to a bonefurther comprises affixing the pattern plates to opposing sides of abone.
 14. The method of claim 11 wherein the step of traversing thecutting means along the cutting path comprises the steps of grasping ahandle interconnected with the cutting means and guiding the cuttingmeans along the cutting path by manipulating the handle.
 15. The methodof claim 11 for resecting a femur further comprising the step aligningthe pattern means along a side of a distal femur.